Our overall research goal is to investigate the long-term performance of zeolite/polyamide nanocomposite reverse osmosis membranes for purification of brackish water.

Specific questions we will investigate are:1. Will a thin-film polyamide/zeolite nanocomposite membrane maintain acceptable flux and rejection on pretreated agricultural drainage water after a minimum of three months of continuous operation? 2. How, if at all, will the membrane's performance (water permeability and salt rejection) change over that time? 3. Will the zeolite nanocrystals disperse from or wear out of the membrane? 4. Will the membranes foul to a greater or lesser degree than similar industry controls? 5. Can the zeolite/polyamide nanocomposite membranes be cleaned (to minimize or reduce fouling) in the same manner that commercial membranes are?

Work has been underway since 2007 to develop thin-film nanocomposite, or mixed-matrix, membranes for water purification through reverse osmosis. In 2010, UCLA researcher Eric Hoek noted that although super-hydrophilic and anti-microbial nanoparticles are available to use in casting fouling-resistant nanocomposite UF membranes, "the fundamental relationships between inorganic filler material size, chemical composition, and structure and the resulting mixed-matrix membrane transport, structural, mechanical, and interfacial properties are not well understood." This same information applies to mixed-matrix nanocomposite zeolite/polyamide RO membranes.

While there are published studies on long-term performance of polyamide/zeolite reverse osmosis membranes on recovery of seawater, there are no published studies on these membranes' performance on brackish waters (total dissolved solids < 3000 ppm). Work in 2007 identified a mixed-matrix membrane formula that produced brackish-water type performance, but there are no published reports on long-term (>48 hour) testing of these types of membranes.

Need and Benefit

Water purification with osmotic membranes has a continual demand for higher-efficiency membranes with increased durability. Zeolite/polyamide nanocomposite RO membranes have demonstrated the potential to address these demands, based on laboratory testing to date. The specific need is to identify whether a mixed-matrix nanocomposite membrane can be formulated that can treat real-world water, in an operating plant environment, for a representative length of time (e.g., a minimum of three months), because there are no reports in the scientific literature on this.

The most critical benefit of the proposed research is that it will add new information to the exisiting body of scientific knowledge about mixed matrix membranes for water purification. If the membranes being tested have acceptable long-term performance, then the basis exists for new membrane formulation which can be optimized and ultimately commercialized. The ultimate impact of the work is to increase the available technology options for reclaiming and purifying water supplies, with reduced energy demands for that activity.

Published accounts of performance testing of mixed-matrix membranes using nanosized zeolites indicate that testing has occurred on laboratory waters, with the membranes compacted for generally less than 24 hours, and operated for a short period of time (30 minutes) after feedwater flows stabilize (Jeong, 2007; Lind, 2009-2011). Data from these tests indicates that the membrane formulas produce hydrophilic, somewhat bacterially-resistant membranes that result in higher flux and similar rejection to commercial membranes; however the flux and rejection performance of the nanocomposite membranes vary as a function of the type, size and concentration of nanoparticles present in the test membrane. Ongoing research in the Lind Lab at ASU is investigating the mechanisms governing transport through nanocomposite membranes.

Contributing Partners

None

Research Products

1. 2 peer reviewed research publications - targeted for journals such as Desalination and the Journal of Membrane Science; these will discuss the testing strategy, methods and materials, and results.2. Final report describing the test processes and results.3. 2 Conference presentations - targeted for North American Membrane Society and the American Membrane Technology Association/American Water Works Association Membrane Technology Conference.